In known fuel tank inerting systems an inert gas such as nitrogen is introduced into the tank ullage to render the tank ullage noncombustible and to pressurize the tank, said inert gas diluting the oxygen released from the fuel as during ascent of the aircraft and purging the same through the tank vent, and said inert gas also maintaining the tank ullage at pressure exceeding ambient pressure as during descent of the aircraft to prevent entry of air into the tank through the vent. For fuel tank inerting systems of the type just described, reference may be had to the following patents:
3,587,618 3,710,549 3,590,559 3,732,668 3,628,758 3,788,039 3,691,730 3,788,040 3,693,915 3,830,307
In the U.S. Pat. Nos. 3,587,618, 3,590,559, 3,693,915, 3,710,549, 3,732,668, and 3,788,039 the fuel with oxygen dissolved therein is scrubbed during flight. In the first two of the patents mentioned, inert gas such as nitrogen is bubbled through the fuel in the aircraft fuel tank as the aircraft ascends, the liberated oxygen being diluted by admission of inert gas into the ullage and venting through the fuel tank vent valve and in the remaining patents fuel in the tank is recirculated and mixed with inert gas to liberate oxygen from the fuel for dilution and venting by inert gas introduced into the tank ullage.
In the U.S. Pat. Nos. 3,628,758, 3,691,730, 3,710,549, 3,732,668, and 3,788,040, it is contemplated to scrub the fuel containing dissolved oxygen therein in the aircraft fuel tank while the aircraft is on the ground being refueled, the scrubbing equipment being duplicated in each aircraft and the inert gas is supplied into the tank ullage from the airborne inert gas supply to dilute the liberated oxygen and to vent the ullage through the fuel tank vent valve.
In all of these known expedients, the scrubbing equipment is in the aircraft fuel tank itself and hence must be duplicated in each aircraft.